1. Field of the Invention
The invention concerns the manufacture of a superconductor consisting of a large number of filaments.
To be more precise it consists in a method of manufacturing a stable multifilament superconductor with reduced losses, which method is faster and more economic than prior art methods.
2. Description of the Prior Art
Two problems must be solved in manufacturing a superconductor, namely improving the stability of the superconductor and reducing losses.
Depending on the intended uses, the emphasis is given to one or other of these requirements by varying the composition of the matrix.
There are at present two techniques for manufacturing a multifilament superconductor and each has its own advantages and disadvantages. The two techniques are described briefly hereinafter with reference to FIG. 1 of the accompanying drawings.
The double stacking technique necessitates three steps:
stage 0: manufacture of monofilament rods by extruding and drawing billets containing a superconductor alloy in a matrix (in the example shown, NbTi alloy, Cu matrix); PA1 stage 1: assembling a large number of monofilament rods (generally less that 1000) in a matrix tube (Cu in this example); PA1 stage 2: assembling a large number of multifilament rods (generally less than 1000) in a matrix tube (Cu in this example). PA1 stage 0: manufacture of monofilament rods by extruding and drawing billets containing a superconductor alloy in a matrix, as in the previous technique; PA1 stage 1: assembling monofilament rods, the number of which is equal to the number of filaments in stage 2 referred to above, in a matrix tube (Cu in this example).
The superconductor is then subjected to the usual finish drawing, heat treatment, twisting and sizing processes.
The above technique provides superconductors with matrix channels within the filament area. These channels are the matrix tube in which the monofilament rods are assembled in stage 1. The presence of the channels increases the heat stability of the wire and enables the level of losses by coupling in the filament area to be controlled. However, the technique is costly and has a low yield.
The single stacking technique necessitates only two steps:
The superconductor is then subjected to the usual processes, as in the previous technique.
The single stacking technique is less costly and has a higher yield than the double stacking technique but the absence of matrix channels between bundles of filaments limits the heat stability of the conductor and the possibility of controlling losses by coupling, as obtained with the double stacking technique.
FIG. 2 of the accompanying drawings shows the cross-sections of a single stacking superconductor and a double stacking superconductor each with .times.100 and .times.1000 magnifications. The superconductors are intended to be used in the manufacture of the conductive inner layer of a bipolar magnet of a particle accelerator. In these superconductors the matrix (Cu)/superconductor (Sc) ratio is 1.9.
The figure enables a comparison of the two techniques described hereinabove. It shows in particular (.times.1000 magnification) the existence of Cu channels in the double stacking superconductor and their absence in the single stacking superconductor.
The aim of the invention is to provide a method of manufacturing a multifilament superconductor having improved heat stability and enabling the level of losses by coupling to be controlled, as compared to a superconductor manufactured by the single stacking technique, with reduced costs and increased yield compared to the double stacking technique.
In accordance with the invention, the above aim is achieved by a single stacking process that produces a superconductor having a cross-section similar to that of a superconductor obtained by the double stacking technique.